Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
Network Synchronization Challenges in 5G
Bashar Abdullah
RSP Product Line Architect
March 30, 2021
WSTS Virtual Conference 2021
2Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
Time?
Time is a complex measure, guide and standard that has
laymen and experts, spanning many disciplines, defining,
understanding and applying it. It is therefore not surprising
that its representation and interpretation may change
meaning depending on its context and application.
– Bashar Abdullah
3Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
4Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
Management
5G Packet Network Synchronization Overview
Fronthaul Midhaul Backhaul
4G LTE FDD
Planner/
Controller/
Orchestrator
MECFrequency
Frequency+
Phase+Time
Clock Source & Trail
5G NR
5G NR
4G LTE TDD
& LTE-A/ProMassive
MTC
URLLC
eMBB
5Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
• ePRTC (GNSS trained atomic)
• PRTC (GNSS only)
• G.8275.1 Full Timing Support (FTS)
• G.8275.2 Partial Timing Support (PTS)
• 802.1AS Time Sensitive Networking PTP (TSN PTP)
• Proprietary Profiles
• GNSS & G.8275.1 Assisted Full Timing Support (AFTS)
• GNSS & G.8275.2 Assisted Partial Timing Support (APTS)
• Interworking between profiles
• G.703 1pps (phase only)
• G.703 ToD (e.g., NMEA 0183) (time only)
✓ RU, BBU/vBBU, DU/vDU and CU/vCU reference
✓ For 1914.3 reference
Synchronization Landscape for the Next Generation
• G.8262 SyncE
• G.709
• G.8265.1
• IEEE 1914.3
• CPRI
• 10MHz
• BITS
✓ RU and BBU reference
✓ For phase holdover
Frequency Only Frequency, Phase & Time
Synchronization Network
Management & Planning
Controller/Orchestrator
6Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
Synchronization
MEC
FTS
APTSPTS
AFTST-GM
T-TSC
T-BC
T-GM
T-TSC
T-TSC
T-BC
T-BC
T-BC
T-BC
T-TSC
FTST-BC
FTS
FTS
Fronthaul Midhaul Backhaul
FTS
T-BC
T-TSC
eCPRI
O-RAN
Ethernet
CPRI
DU
CUFTS1588v2 Telecom Grand Master
With or Without EEC
RoE timestamps/sequence
numbers
T-GM
T-BC
T-TSC
1588v2 Telecom Boundary Clock
With or Without EEC
1588v2 Telecom Time Slave Clock
With or Without EEC
1588v2/SyncE Freq/Phase/Time
Physical Freq/Phase/Time
Frequency Only
Management
Planner/
Controller/
Orchestrator
T-BC
7Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
• 5G disaggregated architecture with shared
infrastructure
• Fronthaul• O-RAN to CPRI interworking
• CPRI RoE emulation
• Increased RU density
• Midhaul• MEC with vDU/vCU/vBBU
• Increased RU density will expand MEC scale
• Backhaul• Network dimension with a packet fronthaul can easily
exceed engineering limits for SyncE and telecom
profiles
• Network re-arrangements can exacerbate network
dimensioning challenge
➢O-RAN LLS-C1/C2/C3/C4 sync architectures
➢CPRI RRH clock alignment to the O-DU can use 1588v2 re-timing
➢CPRI RoE emulation can make use of 1588v2 as a common
reference at the mapper/demapper functions
➢RU densification can leverage more cost efficient 1588v2
distribution
➢MEC can use hardware enabled 1588v2 NICs to achieve 3GPP
sync performance requirements
➢MEC scale can expand using switch/router NIC-based 1588v2 T-
BCs
➢Position the clock sources in the C-RAN hub or closer to the RUs
where AACs are non-viable for clock distribution
➢Network planning and orchestration can facilitate pre-emptive
network re-arrangement avoidance
Network Architecture, Dimension & Scale
• Fiber deployments
• Transmit and receive paths through
synchronization equipment
• OTN transponders, amplifiers & coherent optics
➢Measure the asymmetry and apply compensation to timing trails
➢For coherent optics, leverage the optical supervisory channel (OSC)
➢Design components and devices that exhibit less asymmetry
Timing Trail Asymmetry
8Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
• Packet network queuing/scheduling/shaping
induce PDV
• Clock distribution across AACs for out-of-region
access to RUs
➢Minimize network PDV by increasing CoS for 1588v2
➢Deterministic forwarding➢Time-based scheduling OIF FlexE/ITU-T G.83xx
➢Time aware scheduling IEEE 802.1bv (up to 25GE only)
➢Frame pre-emption IEEE 802.1bu (up to 25GE only)
➢Move clock source closer to the RU site
➢Secure sync-as-a-service SLA from AAC
Network PDV
• GNSS impairments
• Single point of timing failures
➢Use GNSS disciplined atomic clocks in geographically redundant
locations
➢Maintain multiple geographically dispersed GMs with multiple paths
for timing trails to avoid shared fate faults
➢Maintain phase holdover for durations that cover maintenance and
unexpected sync distribution disruptions
Clock Redundancy
9Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
• Changes in the synchronization network may not
correspond to changes in the network topology or
status
• Positioning clock sources based on economic,
geographic, network technologies, and 3rd party
network factors
➢Measure and monitor timing trails (e.g., sample longest or highest
PDV paths)
➢Measure PDV performance to plan timing trails
➢Monitor the quality of the clock as it traverses the network
(timing trail topology) for each of frequency, phase and time-
of-day
➢Correlate network re-arrangements due to faults or optimizations
with timing trail re-arrangements to be able to anticipate
synchronization network impairments to minimize their impact
Planning, Management and Orchestration
• GNSS impairments are frequent and can be
regional in impact
• Transport network re-arrangements
• PRTCs require periodic maintenance
➢GNSS jamming filters or multi-band receivers
➢GNSS disciplined atomic clocks (i.e., ePRTC) in geographically
redundant locations
➢PRC traceable physical methods (e.g., SyncE)
➢PRC traceable packet methods (e.g., G.8265.1)
Phase Holdover
10Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
Summary
• 5G network synchronization inherits many well known challenges from
previous generations, and introduces some new ones. The new landscape
of synchronization technologies and architectures are enabling the ability to
advance the 5G network evolution.
Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
Thank You
Bashar Abdullah
RSP Product Line Architect
12Copyright © Ciena Corporation 2021. All rights reserved. Proprietary information.
Abbreviations
Abbreviation Expansion
AAC Alternative Access Carrier (wholesale service provider)
AFTS Assisted Full Timing Support (e.g., GNSS primary + G.8275.1 backup)
APTS Assisted Partial Timing Support (e.g., GNSS primary + G.8275.2 backup)
AR Augmented Reality
BBU Baseband Unit
CoMP Coordinated Multipoint
CU Centralized Unit (5G architecture)
DCO Digital Coherent Optics
DU Distributed Unit (5G architecture)
eMBB Enhanced Mobile Broadband
FDD Frequency Division Duplexing carrier signal
FTS Full Timing Support (e.g., G.8275.1)
GNSS Global Navigation Satellite System
LLS-C1/2/3/4 O-RAN Low Layer Split – Synchronization Architectures (C1, C2, C3, C4)
LTE 4G Long Term Evolution RRH
LTE-A 4G Long Term Evolution - Advanced RRH
MIMO Multiple Input Multiple Output
mMTC Massive Machine-Type Communication
NR 5G New Radio
Abbreviation Expansion
OSC Optical Supervisory Channel
OTDOA Observed Time Difference of Arrival
PTS Partial Timing Support (e.g., G.8275.2)
RAN Radio Access Network
REC Radio Equipment Controller
RRH Remote Radio Head
RU Radio Unit
TDD Time Division Duplexing carrier signal
urLLC Ultra-Reliable Low Latency Communication
VR Virtual Reality